Removing entries from a HashMap in an elegant way

HashMap


There are a few solutions for looping a HashMap, but one of the most elegant looks like below:

 

 

01.HashMap<String, Integer> map = new HashMap<String, Integer>();

02.  map.put("One", 1);

03.  map.put("Two", 2);

04.  map.put("Three", 3);

05.  map.put("Four", 4);

06.  map.put("Five", 5);

07.  map.put("Six", 6);

08.  map.put("Seven", 7);

09.  map.put("Eight", 8);

10.  map.put("Nine", 9);

11.  map.put("Ten", 10);

12.          

13.  for (Map.Entry<String, Integer> entry : map.entrySet()) {

14.       System.out.println(map.getKey() + "    " + map.getValue());      

15.  }

 

 

Now, that is great, but if you try to remove an entry while looping

 

 

1.  for (Map.Entry<String, Integer> entry : map.entrySet()) {

2.     if(entry.getValue() > 5){

3.        map.remove(entry.getKey());

4.      }

5.}

an java.util.ConcurrentModificationException will occur!
Solving this issue involves adding an Iterator which conforming to documentation “Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics.” will allows us to call remove(). Therefore, here it is:

 

 

1.for(Iterator<Map.Entry<String,Integer>>it=map.entrySet().iterator();it.hasNext();){

2.     Map.Entry<String, Integer> entry = it.next();

3.     if (entry.getValue() > 5) {

4.          it.remove();

5.     }

6. }

 

 

Done !

Reference